Olfaction in vertebrates begins with the interaction of odor molecules with specific odorant receptors on sensory neurons. Each sensory neuron expresses only one or a few odorant receptors and therefore is functionally distinct. How is the specific identity of each sensory neuron determined? The experiments in this proposal address this issue by analyzing odorant receptor expression during Sensory neuron regeneration in catfish. Through an analysis of the expression of odorant receptor genes at different stages of olfactory neuron differentiation, these experiments will allow an understanding of whether the identity of a sensory neuron is determined through specific lineages from a precursor stem cell through stochastic gene activation during neurogenesis, or by retrograde signals from external factors, such as from the olfactory bulb.